1. Field of the Invention
This invention relates to metal grinding machines and, more particularly, to a grinding machine for automatically removing a surface layer of material having a precisely selected thickness from elongated metal workpieces in preparation for a subsequent operation.
2. Description of the Prior Art
Semi-finished, elongated workpieces such as steel slabs or billets are invariably coated with a fairly thin layer of oxides or other impurities which may extend into the billet a considerable distance and defects consisting usually of longitudinal cracks at localized points on the surface of the billets. These impurities must be removed before the billets are rolled into finished products since the impurities and defects would otherwise appear in the finished product. Cracks particularly must be removed as subsequent operations invariably enlarge them. Billet grinders utilizing a reciprocating carriage for moving the billet longitudinally beneath a rotating grinding wheel or for moving the grinding wheel longitudinally above the billet have long been used to perform these functions. The relatively thin layer is removed by a "skinning" procedure in which the billet reciprocates beneath the grinding wheel with the grinding wheel moving transversely after each reciprocation or grinding pass until the entire surface of the billet has been covered. Relatively deep impurities and defects are then visually apparent, and they are removed by a "spotting" procedure in which the grinding wheel is held in contact with the localized area until all of the impurities have been removed.
Various techniques have been devised to automate the skinning procedure by automatically reciprocating the billet beneath the grinding wheel and moving the grinding wheel transversely an incremental distance each grinding pass until the entire surface has been covered. The basic problem with these systems has been their inability to remove a constant depth of material at a rapid rate particularly from non straight workpiece surfaces thus either severely limiting the speed at which workpieces are conditioned or removing an excess quantity of metal from workpieces. These problems are principally due to excessive wheel vibration caused by exposure of sliding ways to abrasive environment and resulting wear which reduces grinding wheel contact with the workpiece and the use of control systems having a relatively slow response time which are thus incapable of responding to irregular workpiece surfaces at a sufficient rate.